Cardiovascular (CV) diseases, such as hypertension and coronary heart disease, are major health problems in the United States. Attempts to account for the development of CV disease have applied the risk factor approach and there is general agreement that the reduction of risk factors is the major goal of any program for the prevention of CV disease. An increasing body of evidence supports the concept that CV reactivity is a marker and possibly an important risk factor in the evolution of CV disease. Evidence indicates that indices of cardiac function and performance, particularly left ventricular (LV) mass, predict subsequent CV morbidity and mortality. Investigators have shown that only some individuals will demonstrate a change in blood pressure when sodium intake is altered, i,e., some people are salt-sensitive and some are salt-resistant. Interactions among CV reactivity, cardiac indices, and salt-sensitivity are unknown. Based upon our studies 1) of reactivity (over 1,000 healthy children) we have defined hypo- and hyperactivity, 2) blood pressure responses to sodium we have defined salt-sensitivity, and 3) of clinical pediatric cardiology we have performed thousands of echocardiaograms, The objectives of the present investigation are 1) to examine cross- sectionally the interactions among CV reactivity, cardiac indices, and salt-sensitivity; 2) to determine longitudinally the two-year stability of these measurements, and 3) to evaluate the power of the initial measurements to predict the follow-up measurements. These measurements will be performed in the schools among a large biracial follow-up measurements. These measurements will be performed in the schools among a large biracial sample of healthy junior high school students. Specifically, we will select a cohort of 320 children who are hyper- or hyporeactive to the stress of a television video game. Subsequently, echocardiograms will be obtained and children will consume a low-sodium diet for 1 week. All measurements will be repeated in a w year follow-up study. Thus, we can assess the importance of the factors in the development of CV risk during childhood, the period of life when the precursors of CV disease become apparent. The results of this study may justify the development of new diagnostic procedures for the simple, non-invasive assessment of potentially important risk factors. These new procedures could be incorporated into a program of preventive cardiology screening and prospective intervention studies.